Wideband Code Division Multiple Access (WCDMA) receiver may include a radio unit (RU) and a digital base band unit (DBBU). The RU may include, among other components, an analog filter and a sigma delta analog to digital converter (SD-ADC). The analog filter may be used as anti-aliasing filter (AAF) with limited channel selection capabilities.
The DBBU may include a decimation filter coupled to a matched filter and a power measurement unit to measure a power level of a signal at the output of the matched filter. An automatic gain controller (AGC) may receive the power measurement and may adjust a gain of amplifiers at the RU to achieve optimal signal spread at an input of the sigma-delta ADC.
More specifically, the measurement unit may measure an assigned channel power after the digital matched filter. This measurement may be compared to a predetermined power (e.g., a threshold). The AGC may compensate for the difference between the measurement of the assigned signal and the threshold, by sending a gain command to the amplifiers at the RU. As a result of the RU limited selectivity, high interferences from adjacent channels may be present at the ADC input. The power of these interferences is not reflected in the power measurement at the matched filter output and, thus the gain is not changed and the ADC input signal may be clipped.
Known radio receiver architectures may prevent the undesired effect described above by expanding the dynamic range of the SD-ADC and employing an AGC that leaves a headroom at an upper part of an amplitude of the input signal of the SD-ADC for adjacent channel interferences. However, the known radio receiver architectures may have at least two disadvantages. The first disadvantage may be that the radio receiver architecture requires a sigma delta ADC with a high dynamic range (e.g., ˜70 dB). The second disadvantage may be that a desired signal is always spread over a lower part of the SD-ADC dynamic range where the signal may be more susceptible to implementation impairments.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.